【作者】 蒋强；

【导师】 王暄；

【作者基本信息】 哈尔滨理工大学 ， 电气工程及其自动化， 2014， 博士

【摘要】 近十多年来，太赫兹时域光谱技术已广泛应用于工业生产和科学研究当中，但太赫兹辐射源和探测源一般采用电光晶体，受晶体本身晶格结构和相位匹配的影响，难以获得宽频带和高振幅的太赫兹时域光谱系统。电光聚合物与传统电光晶体相比，具有高的电光系数、大的相干长度以及无声子吸收间隙等优点，使其成为实现此系统最理想和极具应用前景的太赫兹辐射源和探测材料。电光聚合物作为新兴的太赫兹辐射源检测材料虽然优势明显，但受聚合物材料本身性质、极化方式、成膜工艺等限制，高电光系数、良好的生色团取向稳定度以及在太赫兹波段低色散等综合性能优良的材料仍很缺乏。因此，合成高品质的电光聚合物材料，使之能够广泛运用于太赫兹时域光谱系统之中具有重要的研究意义和实用价值。本文以侧链型电光聚合物为主体，通过物理混合方式再掺入一定比例的小电光分子制备了具有双电光分子的聚合物体系。通过强极性的小电光分子的掺入使得作为主体的侧链型聚合物的极性得到改善，使其在外部电场作用下，侧链上的生色团分子更易取向。另外，小电光分子的引入，聚合物体系的生色团分子含量增加，宏观上表现出的非线性光学效应得到增强。电光系数和生色团取向稳定度的测试结果表明，双电光分子聚合物EDB(6wt%)/2,4-二硝基苯胺接枝咔唑聚磷膦(94wt%)的电光系数能达到33pm/V，且在室温下放置600小时后，生色团取向稳定度能够保持在初始值的69%。目前用于太赫兹时域光谱系统中的电光聚合物薄膜探测器件常采用三明治结构，即聚合物夹在两层透明导电氧化物层(常用ITO玻璃实现)之间，或者夹在透明导电氧化物层与金属层之间。这种薄膜器件制备简单，但在实际运用中导电层在太赫兹波段的吸收性和高反性都会影响器件的探测效率和灵敏度。另一方面，这种三明治结构薄膜器件极化电场方向与聚合物薄膜表面垂直，在使用时需要考虑太赫兹脉冲的入射角度。本文利用激光微刻技术在覆有金属薄膜的玻璃衬底上生成了插指电极阵列，制备了具有共面电极结构的薄膜探测器件。由于电极共面，一方面避免了电极对探测灵敏度的影响，另一方面就是极化电场方向与聚合物薄膜表面平行，太赫兹脉冲可以垂直入射，不用考虑入射角度对探测效率的影响，从而提高太赫兹波的探测效率。实验结果表明，在相同薄膜厚度下，共面插指电极结构薄膜器件与三明治结构薄膜器件得到的振幅比约在1.3左右，即探测效率能够提高30%左右。太赫兹时域光谱技术用于聚合物电介质的测试当中，主要是获取样品在太赫兹波段的频谱特性，从而得到样品在太赫兹波段下的折射率、吸收系数等光学特性参数。本文选取了在电介质工程应用领域中常用的低密度聚乙烯(LDPE)及复合物作为测试对象。利用基于共面插指电极结构的双电光分子聚合物薄膜探测的太赫兹时域光谱系统分别得到了LDPE、不同湿度下的LDPE、LDPE复合物等的THz光谱特性。更多还原

【Abstract】 Terahertz time-domain spectroscopy (THz-TDS) technology is widelyemployed in industrial and scientific in the last decade. Current THz technologiesare limited in their frequency response because of phonon absorbance and poorphase matching in crystalline emitters and detectors. In contrast, amorphouselectro-optic (EO) polymer composite materials have the potential for broad-bandwith, spectral gap-free THz emission and detection while requiring arelatively low pump laser power. EO polymer family have become an alternate tocrystalline EO materials have shown higher EO coefficient, greater coherencelength and broader bandwidth free of spectral gaps compared with theircrystalline counterparts. With better EO polymers being developed continuously,it can be envisioned that EO polymers will take a larger role in the near future.Although the EO polymers have a wide range of advantages, but it lacks a kindof material which has excellent comprehensive performance, e.g. higher EOcoefficient, good stability of chromophores orientation degree and low dispersionin the THz frequency because of it is limited in nature of the material itself,poling geometries and processing techniques. Therefore it has importantscientific meaning and practical value to design and synthesis a high qualityfactor EO polymer in order to widely use in THz-TDS system.In this dissertation, side chain EO polymer as the main body and doped in aproportion of small EO molecule is prepared into double EO molecule polymersystem. With the introduction of the strong polarity molecules, the polarity of theside chain EO polymer as the main body can be improved, so the chromophoresin the side chain molecules can be easier to orientation under the external electricfield. Increase the number of chromophores polymer system because of the Because of the addition of small EO molecule, the macroscopic nonlinear opticaleffect will be enhanced. Through the EO coefficient and chromophore of stabilitytesting, the EO coefficient of EDB(6wt%)/2,4-dinitraniline-carbazole-plyphosphazenes(94wt%) is33pm/V and its stability of chromophore keeps inthe initial value of69%after600hours at room temperature.Up to now, using an EO polymer sensor to detect THz radiation, a polymerfilm is sandwiched between two poling electrodes, which consist of eitherevaporated gold or a transparent conducting oxide (TCO), such as indiumtinoxide (ITO) or TCO-TCO. This thin-film device is easy fabrication, but thedetection efficiency and sensitivity are limited in their structure due to theabsorbability and high reflectivity of metal in the THz regime. On the other side,the poling direction of the device is normal to the polymer plane, therefore to beused it needs to consider the incident angle. In this dissertation, we adopted lasermicromachining technique to deposite interdigitated coplanar electrodes on thealuminum evaporated glass substrate and preparated the thin film device withnterdigitated coplanar electrodes. Because of the electrodes are in plane, on theone hand, to avoid the influence of electrodes for detection sensitivity, on theother hand, this devices allows for optimal overlap of the THz electric field withthe poling direction of the polymer flim without an external slant angle. Underthe same film thickness, the ratio of the THz amplitude from sensor withinterdigitated coplanar electrodes and sensor with sandwhich structure is1.3,thereby increasing the sensing efficiency by30%.THz-TDS technology is employed in material testing, main objective is toobtain information on the complex refractive index, dielectric constant, andconductivity of the sample in the THz regime. In this dissertation, we selectLDPE and its nanocomposite which widely used in the dielectric engineeringfield, as the research object. To used the Terahertz time-domain spectroscopysystem based on the double EO molecules polymer for Terahertz sensing studyon the THz spectroscopy of the LDPE, LDPE with different humidity, and LDPEnanocomposite.更多还原